The present invention relates to an automatic sheet feeder for a printer, facsimile apparatus or similar image forming apparatus or a scanner for automatically feeding sheets stacked on a tray to a reading section one by one.
In a conventional sheet feeder for the above application, a sheet feeding mechanism and a pickup roller raising and lowering mechanism are arranged at the center of a sheet of maximum size in the widthwise direction. It is therefore necessary to position two side guides at the same distance from the above center, a rack mechanism for causing the side guides to move in interlocked relation to each other, etc. This makes the various mechanisms sophisticated and thereby increases the cost of the sheet feeder. Further, a feed roller shaft and separation roller frame shaft each are required to have a length corresponding to the distance between the outer edge of a sheet of maximum side and a point around the center of the same sheet in the widthwise direction. Such shafts increase the overall weight of the sheet feeder.
Moreover, the side guides for preventing sheet from skewing must be moved in matching relation to the width of the sheet of maximum size. It follows that when the sheets of different sizes are stacked on the tray together, the sheets of smaller sizes are not regulated in width by the side guides at all. Such sheets not only skew, but also degrade reading quality and jam a conveyance path. Therefore, only the sheets of the same size must be selected and stacked on the tray.
Technologies relating to the present invention are disclose in Japanese Patent Laid-Open Publication Nos. 4-277150, 6-329303, 7-41191, 7-61616 and 9-216772 and Japanese Patent No. 2,636,085.